1. Field of the Invention
This invention relates to a magnetometer for use in detecting magnetic signals.
2. Brief Description of the Prior Art
High sensitivity He.sup.3 magnetometers are particularly useful in detecting quasistatic magnetic signals occurring over periods of many minutes, such as the signal produced by a slowly moving magnetic object passing a stationary magnetometer. In the use of such systems, the sensor, as configured in accordance with the prior art, must have a significant component of its axis, as defined by the light beam, aligned with the ambient (earth's) magnetic field during the brief preparation cycle in order for the sensor to operate properly. In fact, the signal size is maximum when aligned with the ambient magnetic field and is zero when at 90 degrees to the ambient magnetic field. He.sup.3 magnetometers of the above general type are described in Pat. No. 3,206,671 with improvements thereof in Pat. Nos. 4,567,439, 4,780,672, 4,814,707 and 4,697,519, the specifications thereof being incorporated herein by reference.
In the conventionally configured He.sup.3 magnetometer, polarization is produced in a cell by a beam of circularly polarized resonant radiation from a He.sup.4 or He.sup.3 lamp or a 10830 Angstrom laser directed along the ambient magnetic field direction for several minutes. The lamp and discharge in the cell are then turned off and the nuclear spins are caused to rotate to a plane perpendicular to the magnetic field. This rotation is accomplished by applying a varying voltage to a pair of Helmholtz coils as described in Pat. No. 4,567,439. The nuclear precession frequency is measured by the AC current induced in a pair of coils near the cell. Two coils are used because, in this geometry, the light beam must be directed perpendicular to the coil axes instead of aligned with the axes. Coupling of energy from precessing He.sup.3 moments into the coils is not as efficient as in the case of a single coil. When the signal decays, the process must be repeated. It is desirable to remove this orientation requirement and also to improve device sensitivity.